In the process of machining helixes for worm gears, a cutting tool having two cutting edges is used. Both of the cutting edges engage the work simultaneously to form the helix. Because the leading cutting edge is moving into the helix, sufficient clearance must be provided so that the side flank adjacent the leading edge does not drag or rub on the helix being formed. Thus, it is usual for the cutting edge angle of the leading edge to be more acute than cutting edge angle of the tailing edge which is moving away from the helix. The acuteness of the leading cutting edge angle means that the leading cutting edge will have less support than the trailing cutting edge.
On the other hand, the leading cutting edge will have a positive cutting rake angle, while the trailing edge has a negative cutting rake angle. The positive cutting rake on the leading edge means that there will be less tool pressure on the leading cutting edge than on the trailing cutting edge. The greater tool pressure on the trailing edge will cause it to wear faster than the leading edge resulting in premature tool failure. Further, the uneven tool pressure might cause some deflection of the tool thereby effecting the accuracy of the final workpiece.
Another drawback associated with prior art tools results from the tool having a fixed geometry. Since a different tool geometry is preferred for different helixes, it is necessary to keep on hand a relatively large number of different tools. Further, the machine must be shut down each time a new job is started so that the tool can be changed.